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In a gas insulated substation (GIS), very fast transient overvoltages (VFTO) are generated, due to switching operations. These transient overvoltages and the associated fast transient currents (FTC) develop transient electromagnetic (EM) fields during its propagation through HT conductor of GIS. The transient EM fields due to these transient voltages/currents may leak out into external environment through discontinuities like SF6 to air bushing, SF6 to cable termination, non-metallic viewing ports, insulated flanges, CT, CVT etc. The conducted/induced voltages on control cables/control circuit due to transient EM fields depend on its frequency components. The frequency components and amplitude of transient voltages/currents during switching operations dictate the frequency components and amplitude of transient fields respectively for a particular GIS configuration. In the present paper, the effect of switching operation on peak magnitude of transient currents and their dominant frequency components at different positions in a 245 kV GIS have been reported.